Day 1 Mix the sponge, using spring water or de-chlorinated water, in a bowl until no lumps remain. Cover and let it sit for two hours at room temperature, then refrigerate overnight, up to 24 hours.

Mix the ingredients for the mother sourdough until a stiff ball can be formed. Wrap in plastic wrap, place in a clean bowl and keep for 12 to 24 hours at room temperature.

Day 2 - Baking Day Place the sponge and the mother sourdough in a bowl, add 5 cups of flour, the potato, sour cream, salt, yeast and water and mix with a dough hook until blended. Continue to knead, adding the rest of the flour to create a medium bodied dough that is still a little sticky. Add more flour as needed (I added 3 tablespoons extra for the rolls in the picture). Knead for a total of about 10 minutes.

Let the dough rest for 20 minutes, knead again for 2 minutes, then let it rest for 10 minutes.

On a lightly floured surface, form dough into rolls.

ounce or 50 gram rolls are pictured. A more usual size is 3 ounce rolls, or 70 to 80 grams. Use a scale, if necessary, to keep the rolls uniform.

Place the rolls on parchment paper. Cover with a damp towel or plastic wrap until doubled in size. This will take 30 to 60 minutes, depending on dough and room temperature.

While the rolls are rising, preheat the oven to 450°F for 30 to 60 minutes. Use a baking stone on the middle rack, if you have one. Place an old pan on the lower rack.

Slit the top of the rolls with a lame or sharp razor blade or serrated knife. If rolls are 2 or more inches apart, they will be crispy on all sides, if they are closer together, they will touch and have softer sides.

Place the rolls in the oven (you may need to bake in two batches), pour a cup of boiling water in the old pan and close the door. If you have a squirt bottle with water, squirt the sides of the oven with water several times in the first 5 minutes. Bake for 20 - 25 minutes, or until golden brown.